Abstract: An actuator for a control valve of a dental syringe having a body including a button having a head larger than the diameter of a passageway in which the actuator is to be installed to actuate a control valve of the syringe, a shoulder closely fitting in the passageway, a shaft smaller than the shoulder and having an O-ring snugly fitted therearound and the O-ring also fitting into a groove provided therefor in the passageway, a valve stem engaging portion and a tapered collar extending from the shaft to the valve stem engaging portion to provide for easy O-ring installation.